Heretofore a number of processes have been developed for retorting oil shale to recover therefrom a synthetic crude oil and/or a more refined oil product depending upon the setup of the particular plant.
It has been found that the shale oil particles, after retorting and separation from the oil product, carry to a greater or lessor extent a deposit of carbon, the carbon being on the surface of the particles and/or in the interior of holes, depressions and the like in the particles themselves.